This invention pertains to systems for maintaining plasma currents in toroidal magnetic confinement devices, and in particular to such systems pertaining to plasma currents of the pulsed nonohmic type.
Operation of Tokamaks and the like toroidal magnetic confinement fusion devices may be classified as having either ohmic or non-ohmic current drive, and as having either continuous or pulsed modes of operation. Practical reactor designs favor the non-ohmic current drive in that ohmic or transformer-driven plasma currents must of necessity operate in a pulsed mode. Steady state (continuous) operation, or as a practical approximation, a very long pulse operation (at least several hours or days), is regarded as essential if fusion reactors are to become an economic reality. Long pulse operation is favored because it limits the metal fatique of structural components arising from the heat stresses inherent in short-pulse devices. A variety of non-ohmic methods have been proposed to drive steady-state toroidal currents in Tokamaks. The most promising methods include current-drive by neutral beams and by radio-frequency waves in three frequency regimes: the lower-hybrid (LHW), the electron-cyclotron (ECRF), and the ion-cyclotron (ICRF) regimes.
While the totally steady state tokamak is, perhaps, most desirable, there are advantages to partly steady state tokamaks. The term "totally steady state" implies that no plasma parameters vary with time. The term "partly steady state" implies that the plasma current is nearly constant, but other parameters may vary. Many advantages of totally steady operation accrue to the partly steady operation; since the tokamak does continuously confine hot plasma, the aforementioned heat stresses will not be as severe as in pulsed operation. Also, there are geometrical advantages arising from avoiding the use of ohmic coils and since the current is nearly constant, refrigeration costs of the superconducting toroidal coils are less than in pulsed operation.
Current generation techniques for operation in partly steady state devices are described herein. These devices are of practical interest since they require less circulating power than a completely steady-state mode of current-drive operation. There is a continuous effort in the art to reduce the average power requirements in toroidal magnetic confinement systems. Recent investigation of rf current-drives has focused upon the ratio of current generated to power dissipated, J/P.sub.d, which is a measure of the steady-state efficiency.
It is therefore an object of the present invention to further improve pulsed nonohmic current drive efficiencies in partly steady-state devices.
It is another object of the present invention to provide a system of steady-state toroidal electric currents in the plasma of a fusion device serving to confine the plasma.
It is another object of the present invention to provide a method of oscillating selected plasma parameters in synchronism with the application of a pulsed nonohmic current-drive.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.